1. Field of the Invention
This invention relates to electronic keyboard operated musical instruments, and in particular it is concerned with a touch responsive keyboard instrument.
2. Description of the Prior Art
An electronic instrument designed to duplicate electronically the percussive qualities of an acoustic piano requires that the tone generators be touch responsive. The force with which the keys are depressed must control the peak amplitude of the corresponding generated musical tone. Velocity sensing devices have been used which are operated by the keyboard switches. These devices have included magnets which move relative to an induction coil thereby generating a voltage that is proportional to the relative velocity between the magnet and the coil. Other velocity sensors include inertial springs and microphones.
In U.S. Pat. No. 4,121,490 entitled "Touch Responsive Electronic Piano" a keyboard operated musical tone generator is described which is touch responsive to the force applied to the keyboard mechanism. The depression of a key operates through a pneumatic transducer to provide an air stream having a velocity proportional to the force applied to the key. A velocity microphone transducer responsive to the velocity of the gas produces an output pulse having a peak amplitude proportional to the peak velocity of the air stream. The voltage pulse is used to control the peak amplitude of a musical tone generated in response to the operation of the key so that a direct relation exists between the force with which the key is operated and the amplitude of the resulting sound generated by the instrument.
A commonly employed velocity sensor is one in which two key contacts are arranged to be actuated in sequence as a keyswitch is depressed. The time interval between the successive closure of the two switches is measured and the result is used to control the initial loudness of a corresponding generated musical tone.
The present invention provides a novel implementation for measuring the time interval between the successive key contact closures for key switches having two key contacts.